Adding test stations to a rotary capacitor electrical tester requires increasing the number of cables which must be routed to the upper contacts of the tester. Having a large number of cables not only increase cost and manufacturing complexity, but it also makes it more difficult for a machine to be changed into a different test sequence after it has been built. It also makes it difficult to pivot the upper contact assembly up and down because the large bundle of cables becomes very rigid.
For every track of every test station, there is coaxial wire that connects to a power source to provide the test voltage for that test channel. For example, on a four track system that has four test stations, there would be a total of sixteen coaxial cables going from the power source to the upper contacts. There are two basic types of test stations: active and passive. The main difference is where the lower contact connects to. For an active station, the lower contact connects to a tri-axial cable which then connects to a leakage current measurement device, such as an Agilent 4349B. There is an additional wire which connects the outer shield of the upper contact coaxial cable to the outer shield of the tri-axial cable to allow return currents to flow back to the power source. For a passive station, the lower contact is simply looped back to connect to the outer shield of the upper contact coaxial cable to allow return currents to flow back to the source. There is no measurement device on a passive station.
In the known configuration, the power source has dedicated outputs for active stations and dedicated outputs for passive station. An active station has a current source output, whereas a passive station has voltage source and a series resistor internal to the power source. To connect to the upper contacts, a cable from the active station output to the upper output is connected, and an identical cable is used to connect to the passive channel upper contacts. The lower contacts of the passive station is simply connected via a terminal block to a wire connected to the outer shield of the upper contacts. The lower contact cable is not coaxial, just a single wire. The lower contacts of the active station is a tri-axial cable which goes to another portion of the system, the Agilent 4349B as illustrated in FIG. 1.